Technology for lithium ion batteries has been developed rapidly in the last twenty years. As a type of new energy resources, lithium ion batteries may have many advantages such as high voltage, high capacity, low consumption, no memory effect, no pollution, small volume, high specific energy, low internal resistance, low self-discharge rate, multiple cycle times, good safety performance, and various choices of volumes and appearance. Therefore, lithium ion batteries have emerged as one of the most important kinds of batteries. Now lithium ion batteries are getting more and more attentions and have been widely used in various kinds of electronic products such as laptops and mobile telephones.
With increasing demands for lithium ion batteries, requirements for their preparation technology have become higher to obtain higher energy density and better electrochemical performance. The trend of battery technology development is to improve capacity, cycle performance, safety performance and high-temperature storage performance of lithium ion batteries.
It is known in the art that the internal volume of a battery may comprise: the volume of the electric core and other structural parts, the volume of the electrolyte and the preserved gas swelling volume. Currently, due to the limitation of injection molding technology for manufacturing the structural parts and the compressibility of the volume of the electric core, residual space may be formed in the battery shell. The presence of the residual space may increase the amount of the electrolyte to be filled. When the battery swells in use, the distance between electrode plates may increase, resulting in elongated ion exchange path, reduced battery cycle performance, and increased manufacturing cost and battery weight. Moreover, the residual space may allow wrinkling of the ion exchange film in the electric core, and the wrinkles thus formed may cause the generation of lithium dendrites and potential safety issues. Furthermore, due to the presence of the residual space, after the electrolyte is filled, the separator immersed in the electrolyte may swell so that the surfaces of the electrode plates and the separator may not be in close proximity, thus affecting the battery capacity.